Air-Accelerated Enantioselective Hydrosilylation of Ketones Catalyzed by Copper(I) Fluoride-Diphosphine Complexes: Investigations of the Effects of Temperature and Ligand Structure

Abstract

The fluorotris(triphenylphosphine)copper(I)-bis(meth­anol) complex-chiral diphosphine system catalyzes the hydrosilyl­ation of several alkyl aryl ketones with moderate to excellent enantioselectivity. An oxygen acceleration effect was observed and led to a practical protocol with low catalyst loading. Optimizations of enantioselectivities (<95%) and catalytic ratio (<0.05 mol%) were obtained with bulky Ar-MeO-BIPHEP ligands.

Key words

asymmetric catalysis - asymmetric hydrosilylation - copper hydride - copper fluoride - oxygen effect

References

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4

Poly(methylhydrosiloxane) (PMHS), MW 1900, a 29mer, with one hydride per monomeric unit, available from various companies. Thus, 0.34 equiv of a 29mer is (0.34 equiv × 29) or ca. 9-10 equiv of hydride per substrate; PMHS is a safe and inexpensive polymer co-product of the silicon industry.

10

See ref. 9 for a typically procedure with degassing system using 3 freeze-pump-thaw cycles, and with CuCl (3 mg, 0.03 mmol, 0.03 mol%), t-BuONa (3.6 mg, 0.036 mmol, 0.036 mol%), (S)-BINAP (18 mg, 0.03 mmol, 3 mol%), and anhyd toluene (4 mL).